Loads of a cool action and funny. Though i'm never going to give in to the idea that it's ok for writers/directors to tell 1/4 of a story and call it complete just because there were some previous books/sequels/back stories that they assume all the viewers already knew about. If i didn't know most of these characters stories already, i'd feel pretty lost, and this would just be a big action movie with little substance.

But if you do know everyone's story (even as far as to recognizing Maria Hill) then it's a pretty fun watch that leaves you wanting more by the end of it. I can't imagine watching it more than twice though. It's the type of movie that's basic (for obvious reasons) so after you get over the thrill of seeing your favorite heroes, one-liners, and sweet action, there isn't much reason to get into it anymore; and you're left praying for a sequel.

See I disagree completely with you on that first point.

They need to STOP devoting so much time and energy to origin stories. Just a little bit for a character, and then establish them through the narrative. Otherwise the movie drags. And that happens in this movie. The first act drags severely.

If you have a well developed/established character like these ones or say Harry Potter and such you shouldn't have to tell their stories to catch up everyone else.